The delivery of therapeutic proteins for clinical use is a major challenge to pharmaceutical science. Once in the blood stream, these proteins are constantly eliminated from circulation within a short time by different physiological processes, involving metabolism as well as clearance using normal pathways for protein elimination, such as (glomerular) filtration in the kidneys or proteolysis in blood. The latter is often the limiting process affecting the half-life of proteins used as therapeutic agents in per-oral administration and either intravenous or intramuscular injection. The problems associated with these routes of administration of proteins are well known and various strategies have been used in attempts to solve them.
A protein family, which has been the focus of much clinical work, and efforts to improve its administration and bio-assimilation, is the cytokine family, including the interferon family. Interferon molecules are grouped in the heterogeneous family of cytokines, originally identified on the basis of their ability to induce cellular resistance to viral infections (Diaz et al., J. Interferon Cytokine Res., 16:179-180, 1996). Type I interferons, referred to as interferons α/β, include many members of the interferon α family (interferon α1, α2, ω and τ) as well as interferon β. The type II interferon γ is different from type I in its particular mechanisms that regulate its production. Whereas the production of interferons α/β is most efficiently induced in many types of cells upon viral infection, interferon-γ is produced mainly in cells of hemopoietic system, such as T-cells or natural killer cells, upon stimulation by antigens or cytokines, respectively. These two interferon systems are functionally non-redundant in the antiviral defense host.
Interferon α, hereinafter “interferon alpha-2b,” or “interferon α-2b” or “IFNα-2b,” used interchangeably, has a broad spectrum of biological effects, including antiviral effects. Antiviral effects include antiproliferative and immuno-modulatory actions (Stark et al., Annu. Rev. Biochem., 67: 227-264, 1998). As well as eliciting strong antiviral activities in target cells, interferons α/β also activate effector cells of the innate immune system such as natural killer cells and macrophages (Pestka et al., Annu. Rev. Biochem., 56: 727-777, 1987; Biron et al., Annu. Rev. Immunol., 17:189-220, 1999). As part of its immuno-modulatory action, interferon type I protects T-lymphocytes from apoptosis (Scheel-Toeller et al., Eur. J. Immunol., 29:2603-2612, 1999; Marrack et al., J. Exp. Med., 189:521-530, 1999) and growth enhancing factors (Robert et al., Hematol. Oncol., 4:113-120, 1986; Morikawa et al., J. Immunol., 139:761-766, 1987). The biological effects of interferons α/β are initiated upon binding to the IFN type I receptor, which results in activation of several downstream effector molecules (Hibbert and Foster, J. Interferon Cytokine Res., 19:309-318, 1999).
Interferons as well as many cytokines are important therapeutics. Since naturally occurring variants have not evolved as therapeutics, they often have undesirable side-effects as well as the above-noted problems of short-half life, administration and bioavailability. Hence, there is a need to improve properties of cytokines, including interferons, for use as therapeutic agents. Therefore, among the objects herein, it is an object to provide cytokines that have improved therapeutic properties.